# Every blue eye from a single individual mutation? Really? **URL:** \ **Category:** Factual Questions\ **Created:** [December 10, 2025, 9:06pm UTC](https://boards.straightdope.com/t/every-blue-eye-from-a-single-individual-mutation-really/1025603 "2025-12-10T21:06:14Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![lissener](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lissener/32/6139_2.png) [@lissener](https://boards.straightdope.com/u/lissener)\ **Post date:** [December 10, 2025, 9:06pm UTC](https://boards.straightdope.com/t/every-blue-eye-from-a-single-individual-mutation-really/1025603/1 "2025-12-10T21:06:14Z")
I’m sure you’ve heard the assertion that everyone who has blue eyes is descended from the same person. Wouldn’t that mean that the mutation occurred only once in all of human history? How likely is that? Every blue-eyed native African shared an ancestor with every native Sámi? What about heterochromians? ---
**Author:** ![zimaane](https://avatars.discourse-cdn.com/v4/letter/z/a3d4f5/32.png) [@zimaane](https://boards.straightdope.com/u/zimaane)\ **Post date:** [December 10, 2025, 9:52pm UTC](https://boards.straightdope.com/t/every-blue-eye-from-a-single-individual-mutation-really/1025603/2 "2025-12-10T21:52:52Z")
> [@lissener](#): > > Wouldn’t that mean that the mutation occurred only once in all of human history? Not necessarily. The mutation could have occured multiple times, but in all but one case, the individual did not have children (or had children who did not have children…) > [@lissener](#): > > Every blue-eyed native African shared an ancestor with every native Sámi? Given thousands of years for the gene to spread, that is certainly plausible. ---
**Author:** ![lissener](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lissener/32/6139_2.png) [@lissener](https://boards.straightdope.com/u/lissener)\ **Post date:** [December 10, 2025, 10:09pm UTC](https://boards.straightdope.com/t/every-blue-eye-from-a-single-individual-mutation-really/1025603/3 "2025-12-10T22:09:34Z")
Both of those hypotheses seem very unlikely to me. And they seem to contradict each other in principle ---
**Author:** ![Babale](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/babale/32/15666_2.png) [@Babale](https://boards.straightdope.com/u/Babale)\ **Post date:** [December 10, 2025, 10:11pm UTC](https://boards.straightdope.com/t/every-blue-eye-from-a-single-individual-mutation-really/1025603/4 "2025-12-10T22:11:00Z")
You have to define “blue eyes”. For example, apparently a number of members of the Ari people in Ethiopia have blue eyes, but this is linked to Waardenburg syndrome. ---
**Author:** ![Miller](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/miller/32/481_2.png) [@Miller](https://boards.straightdope.com/u/Miller)\ **Post date:** [December 10, 2025, 10:25pm UTC](https://boards.straightdope.com/t/every-blue-eye-from-a-single-individual-mutation-really/1025603/5 "2025-12-10T22:25:07Z")
> [@lissener](#): > > Every blue-eyed native African shared an ancestor with every native Sámi? Doesn’t every human share an ancestor with every other human? ---
**Author:** ![Babale](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/babale/32/15666_2.png) [@Babale](https://boards.straightdope.com/u/Babale)\ **Post date:** [December 10, 2025, 10:31pm UTC](https://boards.straightdope.com/t/every-blue-eye-from-a-single-individual-mutation-really/1025603/6 "2025-12-10T22:31:28Z")
> [@Miller](#): > > > [@lissener](#): > > > > Every blue-eyed native African shared an ancestor with every native Sámi? > > Doesn’t every human share an ancestor with every other human?. I assume he meant that every blue eyed native African shares a _blue eyed_ ancestor with every blue eyed Sami. Which doesn’t appear correct, or at least, depends on your definition of “blue eyed”. ---
**Author:** ![Darren\_Garrison](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/darren_garrison/32/92_2.png) [@Darren\_Garrison](https://boards.straightdope.com/u/Darren_Garrison)\ **Post date:** [December 10, 2025, 10:56pm UTC](https://boards.straightdope.com/t/every-blue-eye-from-a-single-individual-mutation-really/1025603/7 "2025-12-10T22:56:54Z")
> [@Babale](#): > > I assume he meant that every blue eyed native African shares a _blue eyed_ ancestor with every blue eyed Sami. > > Which doesn’t appear correct, or at least, depends on your definition of “blue eyed”. That is exactly what is claimed. > **[Blue-eyed humans have a single, common ancestor](https://www.sciencedaily.com/releases/2008/01/080130170343.htm)** > > Everyone with blue eyes inherited a tiny genetic "switch" that dilutes brown pigment in the iris. This mutation, found in all blue-eyed people, emerged 6,000–10,000 years ago, meaning they all share one common ancestor. ---
**Author:** ![Miller](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/miller/32/481_2.png) [@Miller](https://boards.straightdope.com/u/Miller)\ **Post date:** [December 10, 2025, 11:11pm UTC](https://boards.straightdope.com/t/every-blue-eye-from-a-single-individual-mutation-really/1025603/8 "2025-12-10T23:11:13Z")
[This one](https://collegeofphysicians.org/programs/education-blog/behind-blue-eyes-look-genetic-and-cultural-components-propelled-spread-blue-eyed-humans) goes into a bit more detail, and it’s not quite _all_, but very nearly: > [@](#): > > Homo sapiens (modern humans) emerged around 200,000 years ago in Africa, but the mutation that causes blue eyes did not appear until sometime around 10,000 years ago. In a study conducted by Professor Hans Eiberg and a team from the University of Copenhagen, researchers examined mitochondrial DNA from 155 blue-eyed subjects from Denmark, two from Jordan, five from Turkey, and 45 brown-eyed candidates, looking at the locus (specific location or position of a gene) responsible for brown or blue eyes. The result was the discovery that more than 97% of blue-eyed people share the single H-1 haplotype (a group of genes within an organism that was inherited together from a single parent). Eiberg and his team write, “A shared haplotype among blue-eyed individuals is almost perfect and suggests the blue color phenotype is caused by a founder mutation.” This means that the vast majority of people with blue eyes share a single inherited genetic mutation, rather than each person with blue eyes possessing a unique mutation. The study also tested seven blue-eyed Mediterranean individuals unrelated to the Danish participants as a control group. They, too, carried the H-1 haplotype. These individuals with the H-1 haplotype all inherited the same switch at the same location in their genetic coding, whereas, brown-eyed individuals have a number of variations in melanin production and DNA, with brown-eyed phenotypes being spread out between haplotypes H-5 and H-10. In short, almost all blue-eyed people came from a single ancestor, which is proven by the possession of the exact mutation at the same location in their genetic coding. Notably, the study didn’t include any blue-eyed Africans, but I’m guessing stuff like Waardenburg syndrome falls into that 3%. ---
**Author:** ![Babale](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/babale/32/15666_2.png) [@Babale](https://boards.straightdope.com/u/Babale)\ **Post date:** [December 10, 2025, 11:20pm UTC](https://boards.straightdope.com/t/every-blue-eye-from-a-single-individual-mutation-really/1025603/9 "2025-12-10T23:20:25Z")
> [@Miller](#): > > Notably, the study didn’t include any blue-eyed Africans, but I’m guessing stuff like Waardenburg syndrome falls into that 3%. Gotcha, that makes a lot more sense then I assumed that claims of “all” were considering stuff like Waardenburg syndrome to not be “true” blue eyes. That the claim would be made that they _look_ blue, but the underlying cause is different, therefore they aren’t “the same thing” as “true” blue eyes. Which, sure, you could define “blue eyes” to mean something like that, but then “all people with blue eyes due to this specific underlying mechanism caused by this specific mutation” is nearly tautological. ---
**Author:** ![Alessan](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/alessan/32/465_2.png) [@Alessan](https://boards.straightdope.com/u/Alessan)\ **Post date:** [December 11, 2025, 12:18am UTC](https://boards.straightdope.com/t/every-blue-eye-from-a-single-individual-mutation-really/1025603/10 "2025-12-11T00:18:01Z")
Isn’t that how all evolution works? A mutation happens once, and then spreads. ---
**Author:** ![Andy\_L](https://avatars.discourse-cdn.com/v4/letter/a/c67d28/32.png) [@Andy\_L](https://boards.straightdope.com/u/Andy_L)\ **Post date:** [December 11, 2025, 12:31am UTC](https://boards.straightdope.com/t/every-blue-eye-from-a-single-individual-mutation-really/1025603/11 "2025-12-11T00:31:39Z")
Some sites are prone to mutation so that mutations can occur in multiple individuals. Some _traits_ can occur due to multiple different mutations (lactose tolerance occurred multiple times, in different ways). ---
**Author:** ![Der\_Trihs](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/der_trihs/32/233_2.png) [@Der\_Trihs](https://boards.straightdope.com/u/Der_Trihs)\ **Post date:** [December 11, 2025, 12:40am UTC](https://boards.straightdope.com/t/every-blue-eye-from-a-single-individual-mutation-really/1025603/12 "2025-12-11T00:40:53Z")
Also, some important mutations take only the mutation of a single gene, and so are much more likely to spontaneously happen over and over. The mutation that causes sickle cell anemia for example; it happens all over the world, but as it grants malaria resistance it gets selected for in malarial regions despite its downsides (malaria is _nasty)._ ---
**Author:** ![Andy\_L](https://avatars.discourse-cdn.com/v4/letter/a/c67d28/32.png) [@Andy\_L](https://boards.straightdope.com/u/Andy_L)\ **Post date:** [December 11, 2025, 12:46am UTC](https://boards.straightdope.com/t/every-blue-eye-from-a-single-individual-mutation-really/1025603/13 "2025-12-11T00:46:15Z")
By analogy, as far as I know, every person in the world with the last name “Asimov” is descended from Judah Asimov - because he is the one who adopted that spelling of the last name otherwise transliterated as Azimov (or Azimoff) - a simple mutation. If his descendants spread around the world, every one of them will be able to trace their last name back to Judah ---
**Author:** ![Northern\_Piper](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/northern_piper/32/5304_2.png) [@Northern\_Piper](https://boards.straightdope.com/u/Northern_Piper)\ **Post date:** [December 11, 2025, 1:07am UTC](https://boards.straightdope.com/t/every-blue-eye-from-a-single-individual-mutation-really/1025603/14 "2025-12-11T01:07:25Z")
Every person in North America who was born Tremblay at birth (ie not counting people who married someone named Tremblay) are descended from one couple in New France, Pierre Tremblay and Ozanne Achon. [https://tremblay.genealogie.org/ancetr\_a.htm](https://tremblay.genealogie.org/ancetr_a.htm) ---
**Author:** ![Babale](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/babale/32/15666_2.png) [@Babale](https://boards.straightdope.com/u/Babale)\ **Post date:** [December 11, 2025, 1:14am UTC](https://boards.straightdope.com/t/every-blue-eye-from-a-single-individual-mutation-really/1025603/15 "2025-12-11T01:14:04Z")
> [@Alessan](#): > > Isn’t that how all evolution works? A mutation happens once, and then spreads Not always - sometimes similar traits evolve over and over. > **[Books: Improbable Destinies — Jonathan B. Losos](https://www.jonathanlosos.com/books/improbable-destinies)** > > Improbable Destinies: Fate, Chance, And The Future Of Evolution, overturns our assumptions about how evolution works. Earth’s natural history is full of fascinating instances of convergence: phenomena like eyes and wings and tree-climbing lizards... This book really expanded my understanding of how evolution works. It describes a couple of experiments in evolutionary biology, the most notable of which involved anoles in the Caribbean. Long story short: a bunch of Caribbean islands have anole lizards. Anoles come in a wide variety of shapes, colors, and sizes, but on these islands they fell into five or so groups. Some were big and short legged and brown and lived on the trunks of trees; others were small and green and had long legs and lived in the canopies. For a long time, it was assumed that they evolved as you suggest. A mutation happened and the lizards became short legged and brown, well adapted to trunks, and then they spread to the other islands on vegetation rafts or whatever; meanwhile, another anole became green and a high climber, and then spread to all the islands; etc. But when they did genetic studies, they found something fascinating: the different lizard species on each island were _more closely related to other lizard species on the same island than to lizards who looked like them on other islands_. It turned out that each island was colonized by an ancestral population of anoles, who then evolved along one of five or so paths with remarkable regularity. The experiment described in the book took anoles to tiny islands, ones so small that when a big enough hurricane came through they were completely submerged and thus wiped clear of animal life (and so had no anoles). They put a few anoles on each island, and came back after a handful of years (they kept having hurricanes reset their progress so they couldn’t get an interrupted stretch longer than something like a decade) but even in that limited time they were able to show that the anoles they’d catch and measure were noticeably browned and shorter legged if they were living on a trunk, greener and longer legged if they were living high up, etc - in other words, they observed the very beginning of the process of speciation. And it happened in years, not decades. The book shares a number of other examples - guppies who colonize rock pools higher up on their home island after big rainfalls (because there’s enough water coming down the side of the hill that they can swim upstream) and finding pools with no pike cichlids become far more colorful in a handful of generations, for example. Now, what’s interesting is, the book points out that it doesn’t _always_ work that way. It shares another study, one where the _opposite_ happened, closer to our traditional understanding - a mutation happened _only once_ and the only examples of the trait are in daughter populations from that mutation. In this study, they took 12 jars of E coli and grew the bacteria inside, studying how they and how quickly they reproduced. The strains followed similar paths, and when they tested what mutations had occurred and how they impacted the chemistry going on in the jars, they found that the same things were happening across the populations, although at different rates and in different order. And then, after this study had gone on for a long time, many thousands of generations, something completely new happened: one population gained the ability to grow on a new substrate (Citrate) which E coli usually cannot do (in the presence of oxygen, which the jars had). This had happened roughly 30,000 generations in. They went back to frozen samples from prior generations and found that they could “replay” the evolution of this trait, but only if they started with a sample after the 20,000th generation - if they started any earlier, the Cit+ trait never evolved. And almost 20 years later, the same trait never appeared independently again. So it seems as if evolution works quickly and predictably _most of the time_, but every once in a while something that’s truly rare happens and changes the course of evolution in entirely novel ways. I really recommend the book - it blew my mind the first time I read it. ---
**Author:** ![lissener](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lissener/32/6139_2.png) [@lissener](https://boards.straightdope.com/u/lissener)\ **Post date:** [December 11, 2025, 1:33am UTC](https://boards.straightdope.com/t/every-blue-eye-from-a-single-individual-mutation-really/1025603/16 "2025-12-11T01:33:51Z")
In this thread are the only examples seen describing this phenomenon that employ qualifiers. “All,” the only way I’ve ever heard this, is an absolute. “97%” is not. ---
**Author:** ![LSLGuy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lslguy/32/5813_2.png) [@LSLGuy](https://boards.straightdope.com/u/LSLGuy)\ **Post date:** [December 11, 2025, 1:38am UTC](https://boards.straightdope.com/t/every-blue-eye-from-a-single-individual-mutation-really/1025603/17 "2025-12-11T01:38:30Z")
Of course “all” isn’t really as simple as just “all”. “All” is actually “All for the definition of the condition (blue eyes in this case) the author is implicitly using, and ignoring all exceptions, known and unknown, about which this particular author is ignorant.” Lotta ways for digging into the details to discover that “all” is only superficially 100%, not actually 100%. ---
**Author:** ![SunUp](https://avatars.discourse-cdn.com/v4/letter/s/ea5d25/32.png) [@SunUp](https://boards.straightdope.com/u/SunUp)\ **Post date:** [December 11, 2025, 1:42am UTC](https://boards.straightdope.com/t/every-blue-eye-from-a-single-individual-mutation-really/1025603/18 "2025-12-11T01:42:06Z")
> [@Andy\_L](#): > > By analogy, as far as I know, every person in the world with the last name “Asimov” is descended from Judah Asimov - because he is the one who adopted that spelling of the last name otherwise transliterated as Azimov (or Azimoff) - a simple mutation. Is this how Isaac got the idea for “Spell My Name with an S”? ---
**Author:** ![Andy\_L](https://avatars.discourse-cdn.com/v4/letter/a/c67d28/32.png) [@Andy\_L](https://boards.straightdope.com/u/Andy_L)\ **Post date:** [December 11, 2025, 2:00am UTC](https://boards.straightdope.com/t/every-blue-eye-from-a-single-individual-mutation-really/1025603/19 "2025-12-11T02:00:30Z")
Yes, it was ---
**Author:** ![Northern\_Piper](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/northern_piper/32/5304_2.png) [@Northern\_Piper](https://boards.straightdope.com/u/Northern_Piper)\ **Post date:** [December 11, 2025, 2:07am UTC](https://boards.straightdope.com/t/every-blue-eye-from-a-single-individual-mutation-really/1025603/20 "2025-12-11T02:07:04Z")
Previous threads on topic (including one started by OP of this thread three years ago) : > [@Why blue eyes?](https://boards.straightdope.com/t/why-blue-eyes/718718): > > Looking at the map of the distribution of blue eyes in Europe made me wonder: why do Europeans have blue eyes? Were they found in other parts of the world before European expansion and inter-marrying? [https://unsafeharbour.files.wordpress.com/2012/02/maps-europelighteyes.jpg?w=584](https://unsafeharbour.files.wordpress.com/2012/02/maps-europelighteyes.jpg?w=584) > [@How are blue eyes adaptive?](https://boards.straightdope.com/t/how-are-blue-eyes-adaptive/957203): > > I’ve wondered about this before, but was reminded of it after seeing Nora O’Donnell on the nightly news. For her, and many others, crystal blue eyes are a strikingly attractive feature. But do they serve another purpose? That eye color seems so out of keeping with the rest of color schemes on the outside of the human body. Inform me. > [@All blue-eyed people share one common ancestor](https://boards.straightdope.com/t/all-blue-eyed-people-share-one-common-ancestor/979066): > > This can’t possibly be true. This would mean that the blue-eye mutation happened only ONCE in all of the history of homo sapiens. What am I missing here? [Next page](https://boards.straightdope.com/t/every-blue-eye-from-a-single-individual-mutation-really/1025603.md?page=2)